1. Field of the Invention
The present invention relates generally to the field of infusion pumps. More specifically, the present invention discloses an infusion pump capable of administering a series of dosages of liquid medication.
2. Statement of the Problem
Infusion pumps have been widely used for many years to administer antibiotics and other medications to patients. Syringe-type infusion pumps generally include a piston or plunger that slides within a housing to dispense medication. A valve or flow restrictor regulates the flow rate from the pump. Some conventional infusion pumps are driven by a spring, while other infusion pumps require manual pressure to dispense medication.
Another type of conventional infusion pump is vacuum powered. The pump consists of a fluid chamber and a vacuum chamber. Both chambers are equipped with sliding pistons that are mechanically connected (e.g., by a rod) so that a partial vacuum is created in the vacuum chamber as medication is introduced into the fluid chamber. The fluid chamber can be filled either by injecting medication under pressure, or by exerting a force on the fluid chamber piston to simultaneously draw medication into the fluid chamber and create a partial vacuum in the vacuum chamber. After the medication has been loaded into the fluid chamber, the reduced pressure in the vacuum chamber exerts pressure via the pistons and connecting rod that tends to expel medication from the fluid chamber.
Conventional infusion pumps are designed to dispense a single dose of medication, and then must be reloaded for any subsequent doses. This requires additional effort by the healthcare provider. It may entail extra expense if a new infusion pump is used for each dose, or may increase the risk of contamination if the same infusion pump is reused.
Multi-dose infusion pumps have been used in the past in the healthcare industry. However, the multi-dose infusion pumps in common use have substantial shortcomings in terms of complexity, cost, reliability, and ease of use. For example motor-driven infusion pumps can provide flexibility in terms of regulating a series of dosages to be administered to the patient, but tend to be relatively expensive and are complex to use and maintain.
When using a multi-dose infusion pump, it is desirable to continually administer a very low flow rate of medication between doses. This small continual flow, also known as the KVO (keep vein open) flow, helps to keep the patient""s vein open by preventing clotting or collapse of the vein. This minimal KVO flow should be viewed in contrast to the substantially larger flow associated with a typical dose administered by a multi-dose infusion pump, in which each dose would result from a significant movement of the piston. A need currently exists for an infusion pump capable of providing such a KVO flow between doses.
3. Prior Art
Multi-dose infusion pumps, syringes, and related fluid-dispensing devices that have been used in the past include the following:
Drypen et al. disclose a metering syringe with a plunger having a series of stop surfaces spaced along its length that contact a stop on the syringe tube. The stop surfaces halt forward movement of the plunger at predetermined intervals. The stop surfaces are angularly displaced about the longitudinal axis of the plunger, so that incremental rotation of the plunger permits the plunger to be advanced to the next stop surface.
Ishikawa discloses a medical liquid injector for continuous transfusion that includes a syringe fitted with a piston having a detachable shaft rod, and a cap that can be connected to the proximal end of the syringe. The cap has an elastic pressing device (i.e., a spring) for continuously pressing the piston (after the shaft rod has been removed).
Zdeb discloses an example of a vacuum-powered infusion pump.
Wender et al. disclose a hypodermic syringe having a plunger shaft with a series of horizontal locking grooves. These grooves halt forward movement of the plunger within the syringe barrel at predetermined intervals. At each stop, the plunger must be rotated by 180 degrees to proceed to the next stop.
LeFevre, Gangemi, and Chang disclose examples of spring-powered infusion pumps.
Borchard discloses an apparatus for dispensing a controlled dose of liquid medication that includes a dispenser head which fits over the needle-end of a syringe, and a tube slidably engaged to the dispenser head which encases the piston-end of the syringe. Sliding the tube forward pushes the syringe piston and thereby dispenses liquid from the syringe. The amount of liquid dispensed can be controlled by the pin and slot arrangement between the dispenser head and tube shown in FIGS. 3a and 3b of the Borchard patent.
Raphael et al. disclose a programmed action hypodermic syringe having at least one pin protruding into the bore of the barrel that slidably engages a tracking groove in the plunger.
Vaillancourt discloses an infusion pump powered by an elastomeric bladder.
French Patent No. 2,561,925 discloses a syringe for dispensing a series of doses of medication. As shown in FIGS. 2-5 of this patent, a pin and slot arrangement between the syringe barrel and piston limits the forward motion of the syringe piston and thereby determines the size of each dose. The embodiment shown in FIG. 3 of this patent uses a slot with a series of steps. This embodiment: would require that the piston be rotated slightly before dispensing the next dose.
Oshikubo discloses a repeating liquid dispenser having a tubular main body, an actuating member slidably disposed in the main body, and a pressure button on the end of the actuating member projecting out of the upper end of the main body. A spring-loaded rack and pawl mechanism is used to incrementally dispense a quantity of liquid each time that the actuating member is depressed.
Sanchez discloses a hypodermic syringe for administering a plurality of measured doses that includes a barrel and plunger. The size of each dose is controlled by a pin and track mechanism between the barrel and plunger. The track has a plurality of steps controlling forward motion of the plunger within the barrel.
Bull et al. disclose an aliquant discharge device having a syringe with a plunger and a side arm in the upper section of the syringe barrel. In use, the plunger is withdrawn beyond the side arm and suction draws up a blood sample into the syringe. The plunger is then depressed cutting off the vacuum and trapping a known amount of blood in the syringe barrel. This blood specimen is then aliquoted by means of metal stops affixed to the upper end of the plunger that abut on a series of steps as shown in FIGS. 3A-3E of Bull et al.
French Patent No. 1,156,298 discloses another example of a hypodermic syringe with a track mechanism having a series of steps for controlling forward motion of the syringe piston.
Kapelsohn discloses another example of a syringe with a pin and track mechanism to fix the amount of liquid dispensed.
Mathis discloses a liquid-measuring dispenser with a pin and track mechanism for controlling the amount of liquid dispensed.
The prior art relating to the KVO flow includes the following:
Dawe discloses a syringe having a plunger with a resilient balloon-like diaphragm that stretches to provide a more even pressure as fluid is dispensed. The diaphragm also serves as a visual indicator of over-pressure that might damage the vein.
Binard et al. disclose a syringe having an external flexible balloon in fluid communication with the fluid chamber of the syringe, or a resilient diaphragm within the fluid chamber. The balloon inflates at a predetermined pressure to relieve excessive pressure within the syringe and to provide a visual indicator of over-pressure. Similarly, in the embodiments employing an internal diaphragm, the diaphragm deforms at a predetermined pressure to relieve excessive pressure and to provide a visual indicator of over-pressure.
Leibinsohn discloses a pressure-indicating syringe with a telescoping or collapsible plunger.
Webb discloses a self-aspirating syringe for use in combination with a cartridge ampoule having a rubber diaphragm at its lower end and a slidable rubber piston at its upper end.
Raca discloses a pressure-sensing syringe having a piece of compressible material attached to the face of the piston to provide a visual indicator of the pressure within the fluid chamber of the syringe.
4. Solution to the Problem
None of the prior art references discussed above show a multi-dose infusion pump that provides a KVO function. In particular, the present invention discloses a multi-dose infusion pump having a member (e.g., a resilient diaphragm) extending across the face of the piston that is compressed rearward by pressure within the fluid chamber as the piston moves forward and fluid is dispensed, and then gradually returns to its initial position after forward motion of the piston stops to continue to dispense a small quantity of fluid for a period of time.
This invention provides a multi-dose infusion pump that employs a piston sliding within the internal chamber of a pump housing to dispense liquid from a port. The peripheral surface of the piston has a sequence of steps in a radial pattern spaced at intervals along the longitudinal axis of the chamber. A cap is rotatably mounted to the pump housing and includes a stop that limits forward movement of the piston by engaging a selected one of the steps on the piston at each rotational position of the cap. This causes a series of predetermined quantities of liquid to be dispensed as the cap is rotated to align the stop with each step in sequence. A spring between the cap and piston urges the piston forward in the chamber to dispense liquid from the port. The peripheral surface of the piston can also be equipped with a series of guide surfaces that allow the piston to be fully retracted toward the cap without engaging the steps while the cap is in an initial rotational position, and then guide the stop along the steps in a predetermined order as the cap is rotated through a progression of rotational positions. The forward face of the piston can also be provided with a member (e.g., a resilient diaphragm) that is compressed under fluid pressure as the piston moves forward, and then gradually returns to its initial position after forward motion of the piston stops, thereby continuing to dispense a small quantity of liquid for a period of time between doses.
A primary object of the present invention is to provide a multi-dose infusion pump that is inexpensive to produce.
Another object of the present invention is to provide a multi-dose infusion pump that can be easily used by a healthcare provider with minimal instruction.
Another object of the present invention is to provide an infusion pump capable of providing a minimal continuing flow between doses to help keep the patient""s vein open.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.